In a current LTE (Long Term Evolution) system, uplink and downlink data are scheduled in a one-to-one manner by using a PDCCH (physical downlink control channel) or an E-PDCCH (enhanced-PDCCH). With the development of communications technologies, a capacity of the control channel is challenged by an ultra large quantity of user connections and a potential quantity of concurrently connected users in future communication. Optimization of control channel overheads is becoming an important direction of a future evolved LTE system.
To reduce overheads of a control channel, a group scheduling-based uplink contention transmission solution is developed. A main idea of this solution is: A base station classifies terminal devices into a plurality of contention resource groups; uplink transmission for each contention resource group is initiated by a CB-grant (contention-based grant) sent by the base station; and the base station distinguishes CB-grants of different contention resource groups by scrambling using different CB-RNTIs (contention-based radio network temporary identifier). When a terminal device detects a CB-grant that matches a contention resource group to which the terminal device belongs, the terminal device transmits data on a resource scheduled by the CB-grant.
In this solution, the base station uses one piece of control signaling to schedule a plurality of terminal devices in one contention transmission resource group, and uses DMRS (demodulation reference signal) sequences of terminal devices to distinguish uplink data transmitted by the terminal devices. According to this solution, uplink transmission of a plurality of terminals is made possible by one scheduling. Therefore, scheduling overheads can be reduced.
Although overheads of a control channel can be reduced according to the group scheduling-based uplink contention transmission solution, to ensure orthogonality between DMRSs of different terminal devices, a maximum quantity of terminal devices in one contention transmission resource group is 8. This greatly restricts a quantity of connected terminal devices in an entire system and cannot meet a requirement of a future big connection system for a quantity of connected terminal devices. If a quantity of terminal devices included in a terminal device group exceeds 8, communication quality of the terminal devices is relatively poor.
Therefore, the foregoing data transmission solution has a problem that balance cannot be achieved between a quantity of connected terminal devices and communication quality of the terminal devices.